An automatic transmission for a vehicle automatically converts power generated from a prime mover (such as an engine, an electric motor, or the like) into torque and rotational speeds in RPM that are appropriate for facilitating the driving of the vehicle.
The automatic transmission includes: a torque converter to which the power of the prime mover is supplied; a plurality of operating elements capable of converting the power supplied through the torque converter into torque and rotational speeds in RPM appropriate for driving the vehicle; a plurality of friction elements that engage or disengage rotations of operating elements to implement a plurality of shifting stages; a hydraulic circuit that selectively operates the friction elements by using hydraulic pressure; and a control unit that controls the overall operation of the automatic transmission to selectively adjust the shifting stages depending on a driving state of the vehicle.
A hydraulic circuit for a transmission in the related art may supply oil to at least one of friction elements at a predetermined hydraulic pressure to selectively operate at least one of the friction elements.
To this end, the hydraulic circuit for a transmission in the related art may include: a pump that pumps oil stored in an oil pan; a regulator valve that forms line pressure by adjusting the pressure of the oil pumped by the pump; a reducing valve that receives the oil that has passed through the regulator valve and reduces the line pressure to form reducing pressure; a line solenoid valve that controls the regulator valve by using the reducing pressure; and a proportional control solenoid valve that receives the oil that has passed through the regulator valve and fouls control pressure to selectively control one of the friction elements.
Since the hydraulic circuit for a transmission in the related art controls the friction elements by using the plurality of valves, as described above, the hydraulic circuit has a complex circuit structure. Due to this, the hydraulic circuit for a transmission in the related art has problems in terms of high installation cost and high flow loss.